Rust proofing iron and steel articles



Patented Jan. 31, 1933 UNITED STATES PATENT OFFICE LEO P. CURTIN, 0FGRANBURY, NEW JERSEY, AND BERNARD L. KLINE, 0F BROOKLYN. NEW YORK,ASSIGNORS TO THE WESTERN UNION TELEGRAPH COMPANY, OF NEW YORK, N. Y., ACORPORATION 01' NEW YORK I RUST PROOFING IRON AND STEEL ARTICLES J NoDrawing. Application filed May 22,

.ing of phosphates of iron is formed thereon.

The coating is somewhat porous and its protective properties aresomewhat improved by applying a small amount of a non-volatile oil whichis absorbed in and fills the capillary openings in the coating andrenders it impervious to air and moisture. Iron and steel surfaces havebeen treated with various other acids, such as sulfuric, nitric andoxalic acid, generally for the purpose of cleaning or pickling.Incidentally some preserving action may result from suchtreatment due tothe removal of oxides of iron which act as catalysts promoting theoxidation or rusting. Nitric acid, as is well known, produces an effectknown as passivity, rendering the iron more resistant to oxidation.

The present invention relates to a method of providing iron and steelsurfaces with an adherent protective coating of insoluble oxalates ofiron. As stated, oxalic acid has been used for cleaning the surfaces ofiron and steel objects and is highly efficient for this purpose becauseit reacts vigorously with ferric oxid and ferric salts to produce thehighly soluble ferric oxalate. It is, however, not extensively used forpickling because it is somewhat more expensive than sulfuric acid andother suitable pickling agents.

In accordance with our invention the oxalic acid is not used or onlyincidentally serves as a cleaning or pickling agent, the principalpurpose and effect of the treatment being to form upon the iron or steelsurface a fine grained, strongly adherent and insoluble protectivecoating of an attractive olive green color.

A suitable treatment in accordance with our invention is as follows:

A treating solution is prepared by dissolving 5 parts of oxalic acid(COOH) -2H O .in 100 parts of water and adding to this so- 1931. SerialNo. 539,412.

until a coating of the desired thickness is formed, say 20-25 minutes.The article is then withdrawn from the solution, washed with water anddried. The resulting coating is, as stated, fine grained, stronglyadherent and of an olive green color. It may be oiledwith cleanlubricating oil or painted or lacquered. It provides an admirablesurface for lacquering.

Chemical analysis shows that the coating consists of a complex mixtureof oxalates of iron. The coating is highly insoluble and is not attackedby 10% acetic acid or by strong solutions of sodium acetate, whereas thesimple ferrous and ferric oxalates are quite soluble in acetic acid andare instantly attacked by sodium acetate and converted into the basiciron acetates.

The treatment specified in the foregoing example is capable ofconsiderable variation and is not diificult to control. In general weprefer to use dilute solutions of oxalic acid, but we have found awiderange of concentrations, for example from about 1% to about 10%, .tofunction satisfactorily. The temperature and time of treatment also maybe varied within wide ranges, e. g, from atmospheric temperatures up to100 C. and for periods of from a few minutes up to several hours. Theaction is, of course, more rapid at higher temperatures. For instance,instead of the treatment at 95l00 G. for 20*25 minutes, described above,a similar coating may be obtained by treatment at atmospherictemperature for about 90 minutes. The longer the treatment is appliedthe heavier will be the coating. For instance, in treating an iron orsteel surface to be lacquered or painted, a treatment for 5minutes at95100 C. with the solution describedabove will yield a light coatinghaving excellent rust-proofing properties and providing an admirablesurface to receive the paint or lacquer.

If the surface to be treated carries only a little rust, no preliminarypickling is required because the oxalic acid solution will first actupon and dissolve the oxides of iron present and then act on the cleaniron, liberating hydrogen, 'to produce the insoluble oxalate coatin If,however the iron is coated with mill scale Fe,O.$, it is desirable to've it a preliminary pickling with dilute su furic acid or othersuitable pickling agent.

It is noted that the treating solution illustrated in the foregoingexample contains sulfuric acid and ferric sulfate. These ingredients arenot essential, but it has been found that the presence of a small amountof sulfuric acid is of considerable assistance in speeding up the rateof formation of the coating and also in giving a coatin of a finer grainthan is produced in its a sence, and that the resence of ferric ion inthe trea ing solution also increases the rate of reaction. The ferricion may be added in any suitable form, e. g. as ferric sulfate or aspotassium ferri-oxalate. The presence of phosphate in the treatingsolution has a detrimental effect, tending to produce crystalline,non-adherent coatings.

As stated, the presence of ferric ion in the treating solution isbeneficial. It seems to act as a catalytic agent or oxygen carrier.Salts of copper and tin have a similar effect in speeding the rate ofreaction. Salts of manganese, however, have not been found to give thisbeneficial effect.

The coatings are, as stated above, an attractive olive green color. Thiscolor may be modified by the addition to the treating solution ofsubstances which form colored insoluble iron compounds. For example, theaddition of 1% of potassium ferric cyanide to the oxalic acid solutionproduces a coating of a blue color due to the formation of Prussianblue.

' It will be understood from the foregoing disclosure that the inventionis not to be confused with the use of oxalic acid for cleaning orpickling iron and steel surfaces.

We claim:

1. Iron and steel articles having on their surfaces a fine grained,strongly adherent coating of an olive green color, consisting claim 2 inwhich the solution contains from about to about 1% of sulfuric acid.

4. Process of producing protectivecoatings on iron and steel articles asdefined in claim 2 in which the solution contains a small amount in theneighborhood of 1% of a soluble ferric salt.

5. Process of producing protective coatings on iron and steel articlesas defined in claim 2 in which the solution contains from about to about1% of sulfuric acid and a small amount in the neighborhood of 1% of asoluble ferric salt.

6. A solution for the production ofv protective coatings on iron andsteel articles consisting essentially of water with from about 1% toabout 10% of oxalic acid dihydrate andi from about to about 1% ofsulfuric aci 7. A solution for the production of protective coatings oniron and steel articles as defined in claim 6 in which the solutioncontains also a small amount in the neighborhood of 1% of a ferric salt.

8. A solution for the production of protective coatings on iron andsteel articles consist-' ing essentially of water with from about 1% toabout 10% of oxalic acid dihydrate and a small amount in theneighborhood of 1% of a ferric salt.

In testimony whereof, we aflix our signatures.

LEO P. CURTIN. BERNARD L. KLINE.

of oxalates of iron and being insoluble in 10% acetic acid and strongsolutions of sodium acetate.

2. Process of producing protective coatings on iron and steel articleswhich comprises subjecting a clean metallic surface thereof to theaction of a solution containing from about 1% to about 10% of oxalicacid dihydrate and a relatively small amount of an agentserving toaccelerate the formation of the coating of the group consisting ofsulfuric acid and a ferric salt at a temperature of from about normalatmospheric temperature to about 100 C. for at least about 5 minutesuntil a-coating of the desired thickness is formed thereon.

3. Process of producing protective coatings on iron and steel articlesas defined in 5 DISCLAIMER l,895,56 8. Le0 P. Cumin, Crenbury, N. J.,and Bernard L. Kline, Brooklyn, N. Y. RUST PROOFING IRON AND STEELARTICLES. Patent dated January 31, 1933. Disclaimer filed March 11,1942, by the essignee, The Western Union Telegraph Company. Herebyenters this disclaimer to claim 8 of the patent.

[Ofim'al Gazette April 7, 194 2.]

